Apparatus and method for radiosurgery

ABSTRACT

A method and system is presented for treating moving target regions in a patient&#39;s anatomy by creating radiosurgical lesions. CT scan data representative of a pre-operational diagnostic image of a target region are generated. The plurality of x-rays are generated with an x-ray source. Based on the CT scan data, a treatment plan is generated that defines the requisite beam intensities and paths. The position of the target region is determined in near real time. The composite motion of the target region, due to respiration and heartbeat, is tracked. Signals representative of the change (caused by the composite motion) in the position of the target region at a current time, compared to the position of the target region in the CT scan, are generated. In response, the relative position of the x-ray source and the target is adjusted, so as to account for the composite motion of the target. This process is repeated throughout the treatment. As a result, the x-rays are continually focused onto the target region in accordance with the treatment plan, while the x-ray source tracks the motion of the target region.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority under 35 U.S.C. §19(e) from co-pending, commonly owned U.S. provisional patentapplication Ser. No. 60/477,573, entitled “Apparatus and Method ForRadiosurgery,” filed Jun. 11, 2003. This application also claims thebenefit of priority under 35 U.S.C. § 19(e) from co-pending, commonlyowned U.S. provisional patent application Ser. No. 60,477,551, entitled“Apparatus and Method for Cardiac Treatment,” filed Jun. 11, 2003.

FIELD OF THE INVENTION

[0002] The present invention relates to treatment of lesions whosepositions are significant during the course of treatment, such aslesions located on the heart, or on organs close to the heart. Moreparticularly, the invention relates to a method and system for treatingcardiac-related diseases, and for treating anatomical regions thatundergo motion, such as motion due to pulsating arteries.

BACKGROUND

[0003] A number of medical conditions involve lesions whose positionsare significant during the course of treatment, such as lesions that arelocated on the heart or on other organs close to the heart. In manycases, it is necessary to treat anatomical regions that undergo rapidmotion, for example motion due to pulsating arteries. Traditionally, thetreatment of such lesions or moving anatomical regions has requiredinvasive surgery, such as open heart surgery for cardiac-relatedtreatments.

[0004] As one example, atrial fibrillation is a medical conditioncharacterized by an abnormally rapid and irregular heart rhythm, becauseof uncoordinated contractions of the atria (i.e. the upper chambers ofthe heart.) A normal, steady heart rhythm typically beats 60-80 times aminute. In cases of atrial fibrillation, the rate of atrial impulses canrange from 300-600 beats per minute (bpm), and the resulting ventricularheartbeat is often as high as 150 bpm or above. A curative surgicaltreatment for atrial fibrillation that is known in the art is the socalled “maze procedure,” which is an open heart procedure involvingincisions and ablations of tiny areas of the atria. The surgeon makes aplurality of incisions or lesions in the atria, so as to block there-entry pathways that cause atrial fibrillation. Upon healing, thelesions form scar tissue, which electrically separate portions of theatria, and interrupt the conduction of the abnormal impulses. While thisprocedure can be effective, with a high cure rate, the procedure is longand difficult to perform.

[0005] In general, possible complications of an invasive surgery aresignificant, and include stroke, bleeding, infection, and death. Onetechnique for avoiding the complications of invasive surgery isradiosurgery, which is recognized as being an effective tool fornoninvasive surgery. Radiosurgery involves directing precisely focusedradiosurgical beams onto target regions, in order to create lesions tonecrotize tumorous tissue. The goal is to apply a lethal or otherdesired amount of radiation to one or more tumors, or to other desiredanatomical regions, without damaging the surrounding healthy tissue.Radiosurgery therefore calls for an ability to accurately focus thebeams upon a desired target (e.g. a tumor), so as to deliver high dosesof radiation in such a way as to cause only the tumor or other target toreceive the desired dose, while avoiding critical structures. Theadvantages of radiosurgery over open surgery include significantly lowercost, less pain, fewer complications, no infection risk, no generalanesthesia, and shorter hospital stays, most radiosurgical treatmentsbeing outpatient procedures.

[0006] In order to avoid the disadvantages of invasive surgery, such asthe open heart surgical procedure described above, it is desirable toprovide a method and system for using radiosurgery to treat diseasesthat require the creation of lesions in specifically targeted anatomicalregions. These anatomical regions may be located on a beating heart wallof a patient, or on organs near the heart. Alternatively, theseanatomical regions may be located in other places within the patient'sanatomy that undergo motion, e.g. due to pulsating arteries.

[0007] For these reasons, is desirable to provide a method and system inradiosurgery for precisely applying radiosurgical beams onto thesemoving anatomical regions of a patient.

SUMMARY OF THE INVENTION

[0008] The present invention is directed to the radiosurgical treatmentof lesions whose positions are significant during the course oftreatment, and to the radiosurgical treatment of anatomical regions thatundergo motion. For example, these lesions and/or anatomical regions maybe located on beating heart walls, or on organs near the heart, or onpulsating arteries.

[0009] In accordance with one embodiment of the invention, a method ispresented for treating a moving target in a patient by applying to thetarget one or more radiosurgical beams generated from a radiosurgicalbeam source. The method includes generating a pre-operative 3D scan ofthe target and of a region surrounding the target, the 3D scan showingthe position of the target relative to the surrounding region. Based onthe pre-operative 3D scan, a treatment plan is generated, which definesa plurality of radiosurgical beams appropriate for creating at least oneradiosurgical lesion on one or more targets within the patient.

[0010] In a preferred embodiment of the invention, the target undergoesmotion. For example, the motion may be caused by heart beat and/orrespiration. The movement of the target is detected and monitored. Innear real time, the position of the moving target at a current time isdetermined, and the difference between the position of the target at thecurrent time, as compared to the position of the target as indicated inthe 3D scan, is determined. In near real time, the relative position ofthe radiosurgical beam source and the target is adjusted, in order toaccommodate for such a difference in position. This process is repeatedcontinuously throughout the treatment period.

[0011] In one embodiment of the present invention, a composite motion(caused by respiration and heartbeat, by way of example) of the targetis tracked, and one or more signals are generated that arerepresentative of the motion of the target. For example, a breathingsensor and a heart beat monitor may be used to detect the respirationand cardiac pumping of the patient. Information from the breathingsensor and the heartbeat monitor is then combined, in order to enablethe surgical x-ray source to track the position of the target as itmoves due to respiration and cardiac pumping, and to generate signalsrepresentative of the position of the moving target.

[0012] The signal that represents the composite motion of the target isthen processed to generate two separate signals, each signal beingcharacterized by the frequency of the individual motions that make upthe composite motion. In an embodiment of the invention in which thecomposite motion is due to respiration combined with heart beat, thefirst signal is substantially characterized by the frequency (F1) of therespiratory cycle of the patient, and the second signal is substantiallycharacterized by the frequency (F2) of the heartbeat cycle of thepatient.

[0013] A correction factor is then computed for each signal separately.The correction factor for the first signal is effective to compensatefor the movement of the target due to respiration of the patient. Thepatient's respiratory motion is characterized by a respiratory cycle.The correction factor for the second signal is effective to compensatefor the movement of the target due to the cardiac pumping motion in thepatient. The cardiac motion of the patient is characterized by aheartbeat cycle. Both correction factors are applied to a controllerthat controls the position of the radiosurgical beam source, to modifythe relative position of the beam source and the target, in order toaccount for the displacement of the target due to its composite motion.The surgical x-ray beams are applied from the modified position of thebeam source in accordance with the treatment plan, so that the lesionsare formed at the desired locations in the patient's anatomy. Theprocesses of tracking the motion of the target, computing the resultingdifference in target position, and adjusting the relative position ofthe beam source and the target accordingly, are repeated continuouslythroughout the treatment.

[0014] In use, an observer would see the x-ray source move seemingly insynchronization with the chest wall (i.e. with the respiration), butalso including short pulsating motion corresponding to the heart beatcycle. The x-ray source tracks the movement caused by both respirationand heartbeat, while delivering x-rays to the target in accordance withthe treatment plan.

[0015] In one form of the invention, using techniques similar to thosedisclosed in U.S. Pat. No. 6,501,981 (the “'981 patent”)(owned by theassignee of the present application and hereby incorporated by referencein its entirety), the motion of tissue at or near the target isdetermined. For example, a look-up table of positional data may beestablished for a succession of points along the each of the respiratorycycle and the heartbeat cycle. Motion points for the respiratory cycleinclude position information obtained in response to both respirationand heartbeat of the patient. Positional information for the heartbeatcycle can be obtained through imaging of the tissue while the patient isholding his breath. A table (“table 2) containing this positionalinformation can provide the basis for signal F2. Signal F1, on the otherhand, can be obtained by subtracting data from the table for theheartbeat cycle (obtained by having the patient hold his breath) fromthe data from the composite motion (formed of both respiration andheartbeat), since the resulting table (“table 1”) corresponds to motioncaused substantially only by respiration. Positional changes for thex-ray source can be applied based on superposition of data from table 1and table 2.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 illustrates a radiosurgical treatment system, known in theprior art.

[0017]FIGS. 2A, 2B, and 2C depicts the frequency patterns of the motionof a target region of the patient, caused by respiratory motion (in FIG.2A), cardiac pumping motion (in FIG. 2B) and by a composite motion dueto the combination of the respiratory motion and the cardiac pumpingmotion (in FIG. 2C).

[0018]FIG. 3A provides a schematic block diagram of a radiosurgicalsystem for treating a target region by creating radiosurgical lesions,constructed in accordance with one embodiment of the present invention.

[0019]FIG. 3B schematically illustrates the splitting of the signal(representing the composite motion of the target region into first andsecond signals.

[0020]FIG. 4 provides a schematic flow chart of a method in accordancewith the present invention.

DETAILED DESCRIPTION

[0021] In the present invention, the techniques of radiosurgery are usedto treat target tissue by creating radiosurgical lesions. These lesionsare created in anatomical target regions located in places that undergoconstant motion, such as the heart walls of a beating heart. The motionof the target, due to respiration and heart beat, is continuouslytracked during treatment, so that the radiosurgical beams remainproperly focused and directed onto the desired target regions in thepatient's anatomy.

[0022]FIG. 1 illustrates a radiosurgical treatment system, known in theart. The radiosurgery system 100 shown in FIG. 1 may, for example,represent the CyberKnife system (“CyberKnife”) developed by Accuray,Inc. In overview, the conventional radiosurgery system 100 includes aradiosurgical beaming apparatus 102; a positioning system 104; imagingmeans 106; and a controller 108. The system 100 may also include anoperator control console and display 140. The radiosurgical beamingapparatus 102 generates, when activated, a collimated radiosurgical beam(consisting of x-rays, for example). The cumulative effect of theradiosurgical beam, when directed to and focused onto the target, is tonecrotize or to create a lesion in a target 118 within the patient'sanatomy. By way of example, the positioning system 104 is an industrialrobot, which moves in response to command signals from the controller108. The beaming apparatus 102 may be a small x-ray linac mounted to anarm 112 of the industrial robot 104. The imaging means 106 may be anx-ray imaging system, having a pair of x-ray sources 124 and 125 forgenerating diagnostic imaging beams 126 and 127, and x-ray imagedetectors 136 and 137.

[0023] In the prior art system 100, the imaging means 106 generatesreal-time radiographic images of the anatomical region containing thetarget, by transmitting one or more imaging beams through the target.The controller 108 determines the real-time location of the target, bycomparing the real-time radiographic image with pre-operative CT (orMRI) scans of the target that have been stored within the computer. Thepositioning system 104 manipulates the position of the radiosurgicalbeam, in response to control commands from the controller 108, so as tokeep the radiosurgical beam properly focused onto the target.

[0024] In order to account for the motion of a moving target, forexample due to respiration of the patient, patients have typically beenadvised to hold their breath while being scanned by the CT scanner,prior to treatment. In this way, the moving patient is fixed, andtherefore the scan does not have any motion artifacts. More recently,new radiosurgical devices such as CyberKnife have been employing newtechnologies for treating moving targets. For example, Accuray recentlyrevealed a new product, Synchrony, which is Accuray's new system fordelivering dynamic radiosurgery to tumors that move with respiration.The Synchrony system is described in U.S. Pat. No. 6,501,981 (the “'981patent”), entitled “Apparatus And Method For Compensating ForRespiratory And Patient Motions During Treatment,” which issued on Dec.31, 2002 to A. Schweikard and John R. Adler. The '981 patent is owned bythe assignee of the present application, and is hereby incorporated byreference in its entirety. The Synchrony system precisely tracks tumorsin or near the lungs as they move, enabling highly focused beams ofradiation to destroy the tumors with minimal damage to adjacent normaltissue. In particular, the Synchrony system records the breathingmovements of a patient's chest, and combines that information withsequential x-ray pictures of tiny markers inserted inside or near thetumor. In this way, the Synchrony system enables precise delivery ofradiation during any point in the respiratory cycle.

[0025] In a preferred embodiment of the present invention, the motion ofthe target (located e.g. on the atrial walls of a beating heart) is acomposite motion caused by at least two factors: a) respiratory movementof the patient; and b) rapid pulsation or pumping motion of the heart ofthe patient. FIGS. 2A, 2B, and 2C depict the frequency patterns of themotion of a target within the patient, caused by respiratory motion (inFIG. 2A), cardiac pumping motion (in FIG. 2B) and by a composite motiondue to the combination of the respiratory motion and the cardiac pumpingmotion (in FIG. 2C). The target may be located on a heart wall, or onother moving regions of the patient's anatomy. The respiratory motion ischaracterized by a respiratory cycle, whose frequency (F1) is about anorder of magnitude lower, compared to the frequency (F2) of the cardiacpumping motion. The composite or resultant motion of the target, asillustrated in FIG. 2C, is simply a superposition of the respiratorymotion (shown in FIG. 2A) and the cardiac pumping motion (shown in FIG.2B).

[0026]FIG. 3A provides a schematic block diagram of a radiosurgicalsystem 200, constructed in accordance with one embodiment of the presentinvention, for treating a patient by creating radiosurgical lesions inmoving anatomical regions. The description of FIG. 3A will focus oncardiac-related treatments, although the scope of the present inventionis not limited to cardiac-related treatments, but rather encompasses thetreatment of any anatomical region that undergoes motion, for examplemotion due to pulsating arteries.

[0027] The system 200 includes a CT scanner 212 for generating CT scandata representative of a pre-operative 3-D diagnostic image of theanatomical target, and surrounding tissue. The target is located inthose areas in which the formation of lesions would be therapeutic. Forexample, in the case of atrial fibrillation, the target is located inthose areas in which the formation of lesions would cure atrialfibrillation by properly directing electrical impulses to the AV nodeand onto the ventricles. Because the target undergoes motion due torespiration and cardiac pumping, a plurality of fiducials may beimplanted in the atria near the target, so that the pre-operativediagnostic image shows the position of the target in reference to thefiducials. The pre-operative image is a static image, or “snapshot”, ofthe target and surrounding tissue.

[0028] The system 200 includes a radiosurgical beam source 202 forgenerating one or more radiosurgical beams, preferably x-rays. Thecumulative effect of applying the radiosurgical x-ray beams during thetreatment period is to create at least one lesion in the target, so thatthe desired clinical purpose can be accomplished. In the illustratedembodiment, as in the prior art, the radiosurgical beam source 202 is asmall x-ray linac. The system 200 also includes a surgical beampositioning system 204. As in the prior art, the positioning system 204in the illustrated embodiment is an industrial robot, which moves inresponse to command signals from a central controller 208. The x-raylinac 202 is mounted to an arm of the industrial robot 204. It should benoted that other types of beam source 202 and positioning system 204known in the art may be used, without departing from the scope of thepresent invention. The central controller 208 is preferably amulti-processor computer. The controller 208 may also include a storageunit 218 (for example, for storing the pre-operative CT scan data), andan operator console and display 240. The controller 208 preferably has aplurality of processing or controller units, including, inter alia: 1)treatment planning software 210 for generating, based on the CT scandata generated by the CT scanner 212, a treatment plan that defines aplurality of x-ray beams appropriate for creating one or more lesions inan anatomical target region in the heart; and 2) a controller unit 300for sending command signals to the positioning system 204 (i.e. therobot), so as to adjust the relative position of the beam source 202 andthe target. The treatment plan contains information regarding thenumber, intensities, positions, and directions of the x-ray beams thatare effective to create at least one radiosurgical lesion.

[0029] The system 200 further includes imaging means 206 for generatingx-ray radiographs of the target. The imaging means 206 typicallyincludes a pair of x-ray sources for generating x-ray imaging beams, andan x-ray imaging system. The x-ray imaging system generally includes apair of x-ray detectors (corresponding to the pair of x-ray sources) fordetecting x-rays that have passed through the target, and an imageprocessor for generating an image of the target using the detectedx-rays.

[0030] In the illustrated embodiment, the system 200 further includesmeans for sensing the respiration of the patient and the pumping motionof the heart, and for generating a signal representative of the motionof the target due to respiration and heart beat of the patient. In theillustrated embodiment, the means for sensing the respiration is abreathing sensor 214, and the means for sensing the heart beat is aheart beat monitor 216. In other embodiments of the invention, thesystem 200 may include means for sensing other types of motion of thepatient, for example motion due to pulsating arteries. The breathingsensor 214 may be coupled to an external body part of the patient thatmoves in synchronization with the respiration of the patient, and asensor reader (not illustrated) may be provided that takes a readingfrom the breathing sensor periodically. A number of commerciallyavailable sensors may be used as the breathing sensor 214, includinginfrared tracking systems, force sensors, air flow meters, straingauges, laser range sensors, and a variety of sensors based on physicalprinciples such as haptic, acoustic/ultrasound, magnetic, mechanical oroptical principles.

[0031] In the illustrated embodiment, the system 200 includes a signalprocessor 220 for processing the signal representative of the compositemotion (due to both breathing and heartbeat) of the target region, togenerate therefrom a first signal substantially characterized by afrequency F1 representative of the respiratory motion of the patient,and a second signal substantially characterized by a frequency F2representative of the cardiac pumping motion. Appropriate processingunits in the controller 208, together with the imaging means 206, areused to generate a first correction factor from the first signal, and asecond correction factor from the second signal. The first correctionfactor, when applied to the controller subunit 300, is effective to movethe robot (and hence the x-ray source) to adjust the relative positionof the x-ray source and the target, in a way that accounts for movementof the target due to respiration of the patient. The second correctionfactor, when applied to the controller subunit 300, is effective tocorrect the relative position of the x-ray source and the target, toaccount for movement of the target due to cardiac pumping.

[0032]FIG. 3B schematically illustrates the splitting of the signalrepresenting the composite motion of the target, into first (F1) andsecond (F2) signals, and the generation of the two correction factors.For example, the original signal (representing the composite motion) canbe split into two signals, which are processed separately so as toeliminate a different one of the two components (F1 and F2). Theprocessing could be done by filtering, by way of example. In a preferredembodiment, the original composite signal is treated as a signal plusout-of-band noise. The signal processor 220 may include noise cancelingsoftware for eliminating one or more undesired frequency components,i.e. out-of-band noise. For example, one or more conventionalnoise-canceling algorithms known in the art may be used to cancel theundesired component(s). By way of example, the noise cancelingalgorithms may be effective to extract the undesired component(s), andinvert the extracted components. The algorithm may then generate one ormore signals that cancel out the undesired frequency component(s).

[0033] The first and second correction factors are recombined, andsuperposed, resulting in a combined correction factor. The correctionfactor, when applied to the controller subunit 300, accounts for thecomposite motion of the target due to both breathing and heart beat.

[0034]FIG. 4 provides a schematic flow chart of a method in accordancewith the present invention. In operation, CT scan data are generated instep 310. These data are representative of a pre-operative 3-Ddiagnostic image of the target. Because the target is a moving target,the diagnostic image may show the position of the target with respect toa plurality of fiducials. In the next step 320, a treatment plan isgenerated, based on the CT scan data generated in step 310. Thetreatment plan determines a succession of desired beam paths, eachhaving an associated dose rate and duration, at each of a fixed set oflocations.

[0035] In step 330, the position of the moving target is determined, innear real time. Next, in step 340, the relative position of the beamsource 202 and the target is adjusted to accommodate for the change inthe position of the target, i.e. the difference in the position of thetarget (e.g. determined relative to the fiducials) at the current time,compared to the position of the target in the pre-operative CT scan.Finally, in step 350 surgical x-rays are applied to the target inaccordance with the treatment plan, thereby creating one or more lesionsin the desired locations.

[0036] Because the target is always moving, the step of determining (innear real time) the position of the target includes the step of trackingthe motion of the target. In one embodiment, the step of tracking themotion of the target includes generating at least one signalrepresentative of the motion. In one embodiment, in order to track themotion of the target, the following steps may be taken: 1) the breathingsensor and the heart beat monitor are used to detect the respiration andthe cardiac pumping of the patient, and record information relatingthereto; 2) a plurality of x-ray images of the target and the implantedfiducials are generated in near real time; 3) the recorded informationfrom the breathing sensor and the heart beat monitor are combined withthe plurality of real-times x-ray images, thereby tracking the movementof the target (relative to the fiducials), as the patient breathes andthe patient's heart beats.

[0037] In one embodiment, the signal representative of the compositemotion of the target is split into two signals, and the two signals maybe separately processed through a signal processor, in order to removeundesired frequency components from each signal. A first signal,substantially characterized by a frequency F1 (representing therespiratory cycle of the patient), and a second signal substantiallycharacterized by a frequency F2 (representing the heart beat), aregenerated. A first correction factor is generated from the first signal(F1), and a second correction factor is generated from the second signal(F2).

[0038] In one embodiment of the invention, a look-up table of positionaldata may be established for a succession of points along each of therespiratory cycle and the heartbeat cycle, using techniques similar tothose disclosed in the '981 patent. Motion points for the moving targetinclude position information obtained in response to both respirationand heartbeat of the patient. Positional information for the heartbeatcycle can be obtained through imaging of the tissue while the patient isholding his breath. A table (“table 2”) containing this positionalinformation can provide the basis for signal F2. Signal F1, on the otherhand, can be obtained by subtracting data from the table for theheartbeat cycle (which was obtained by having the patient hold hisbreath) from the data from the composite motion (formed from bothrespiration and heartbeat), since the resulting table (“table 1”)corresponds to motion caused substantially only by respiration.Positional changes for the x-ray source can be applied based onsuperposition of data from table 1 and table 2.

[0039] As explained earlier, the first correction factor accounts forthe breathing motion, and the second correction factor accounts for thecardiac pumping motion. As mentioned earlier, the first and secondcorrection factors are superposed, to generate a combine correctionfactor that can be applied to the controller subunit 300, so that thecomposite motion due to both respiration and heart beat can be accountedfor.

[0040] In another embodiment, the step of generating the first andsecond correction factors may include the step of digitally comparingthe plurality of near real-time x-ray images with the pre-operative CTdiagnostic image. The digital comparison may be done, for example,by: 1) generating one or more DRRs (digitally reconstructedradiographs), using the pre-operative CT scan information together withthe known imaging-beam positions, angles, and intensities; and 2)computing (using one or more processing units in the controller 208) theamount the target must be moved (translationally and rotationally) inorder to bring the DRRs into registration with the real-time x-rayimages. DRRs are artificial two-dimensional images, which show how anintermediate three-dimensional image would appear, if a hypotheticalcamera location and angle, as well as a hypothetical imaging beamintensity, were used. In other words, DRRs are synthetically constructedtwo-dimensional radiographs that are expected to result, if one or moreimaging beams having a known intensity were directed to the target fromcertain known locations and angles. Algorithms known in the art, forexample ray-tracing algorithms, are typically used to syntheticallyreconstruct the DRRs.

[0041] In one embodiment, the step of generating the requisitecorrections (for adjusting the relative position of the x-ray source andthe target, in near real time) to the command signals from the subunit300 may include: 1) extrapolating the detected motion of the target intoa complete cycle; and 2) synchronizing the command signals with theextrapolated motion of the target region, so as to modify the relativepositions of the beam source and the target based on the extrapolatedmotion information. The changes in position of the target is constantlytracked over time, throughout the treatment period. The resultingmodifications in the relative positions of the beam source 202 and thetarget are communicated to the beam source 202 and the positioningsystem 204 by the controller 208. As a result, the position, direction,and intensity of the radiosurgical beams are continuously adjusted, sothat an accurate radiation dose can be applied to the appropriateregions of the patient's anatomy in accordance with the treatment plan,throughout the radiosurgical treatment. The plurality of radiosurgicalbeams remain focused onto the target, in accordance with the treatmentplan, throughout the duration of the treatment, and the radiosurgicalx-ray beam source tracks the movement of the target.

[0042] As an improvement, instead of tracking the changes constantlyover time, the system 200 can, for one component (for example the lowerfrequency component F1 derived from the breathing motion), have arelatively static correction appropriate for just the “peak” of therespiratory cycle, in another embodiment of the present invention. Inthis embodiment, treatment may be performed only at the peaks of therespiratory cycle using the command signals modified by only the staticcorrection factor (from breathing), and a dynamic (constantly monitoredand changing) high-frequency correction factor, derived from heartbeat.

[0043] While the invention has been particularly shown and describedwith reference to specific preferred embodiments, it should beunderstood by those skilled in the art that various changes in form anddetail may be made therein without departing from the spirit and scopeof the invention as defined by the appended claims.

What is claimed is:
 1. A method of treating a moving target in a patientby applying to said target one or more radiosurgical beams generatedfrom a radiosurgical beam source, the method comprising the steps of: A.generating a pre-operative 3D scan of said target and of a surroundingregion, said 3D scan indicating the position of said target relative tosaid surrounding region; B. based on said 3D scan, generating atreatment plan defining a plurality of radiosurgical beams appropriatefor creating at least one radiosurgical lesion on said target; C. innear real time, detecting the motion of said target to determine theposition of said target at a current time, and generating one or moresignals representative of said motion of said target; D. in near realtime, determining the difference in the position of said target at saidcurrent time, as compared to the position of said target as indicated insaid CT scan; E. in near real time, adjusting the relative position ofsaid radiosurgical beam source and said target in order to accommodatefor said difference determined in step D, and applying x-rays to saidtarget from said adjusted position of said radiosurgical beam source. 2.A method in accordance with claim 1, further comprising the step ofsequentially repeating steps C through E during treatment, whereby saidplurality of radiosurgical beams remain focused onto said target inaccordance with said treatment plan throughout the duration of thetreatment, and whereby said radiosurgical beam source tracks saidmovement of said target.
 3. A method in accordance with claim 1, whereinsaid motion of said target is a composite motion that is caused by acombination of: A. respiration of the patient; and B. pumping of theheart of the patient.
 4. A method in accordance with claim 3, whereinsaid step of detecting said motion of said target and generating one ormore signals representative of said motion comprises the steps of A.sensing the respiration and heart beat of the patient, and recordinginformation relating thereto; B. generating in near real time one ormore x-ray images of said target, using x-ray imaging beams having knownbeam paths and intensities; and C. combining said recorded informationwith said x-ray images to generate one or more signals representative ofsaid movement of said target.
 5. A method in accordance with claim 3,wherein the step of generating one or more signals representative ofsaid motion of said target comprises: A. establishing a look-up table ofpositional data for said composite motion of said data, by imaging saidtarget and said surrounding region while the target undergoes saidcomposite motion; B. establishing a look-up table of cardiac motion datafor a succession of points along the heartbeat cycle of said patient, byimaging said target and said surrounding region while the patient isholding his breath; C. establishing a look-up table of respiratorymotion data for a succession of points along the respiratory cycle ofsaid patient, by subtracting said cardiac motion data from saidpositional data for said composite motion of said data; D. generating afirst signal representative of the respiratory motion of said patientfrom the data from said look-up table of respiratory motion dataobtained in step c, said first signal being characterized by a frequencyF1 representative of the respiratory motion of said patient; and E.generating a second signal representative of the cardiac motion of saidpatient from the data from said look-up table of cardiac motion dataobtained in step b, said second signal being characterized by afrequency F2 representative of the cardiac motion of said patient.
 6. Amethod in accordance with claim 4, wherein the step of adjusting therelative position of said radiosurgical beam source and said targetcomprises: A. splitting said signal representative of said movement ofsaid target into first and second signals; B. separately processing saidfirst and second signals to remove undesired components from eachsignal, thereby generating a first processed signal substantiallycharacterized by a frequency F1 representative of the respiratory motionof said patient, and a second processed signal substantiallycharacterized by a frequency F2 representative of the pumping of theheart of said patient; C. generating from said first processed signal afirst correction factor that is effective, when applied to a controllerthat controls the position of said radiosurgical beam source withrespect to said target, to modify the position of said radiosurgicalbeam source relative to said target so as to account for the movement ofsaid target due to respiration of said patient; D. generating from saidsecond processed signal a second correction factor that is effective,when applied to said controller, to modify the position of saidradiosurgical beam source relative to said target so as to account forthe movement of said target due to the pumping of the heart of saidpatient; E. superposing said first and second correction factors,thereby generating a combined correction factor that is effective, whenapplied to said controller, to modify the position of said radiosurgicalbeam source relative to said target so as to account for said compositemotion of said target region caused by both respiration and cardiacpumping.
 7. A method in accordance with claim 6, wherein said firstsignal said second signal are substantially decoupled and mutuallyorthogonal.
 8. A method in accordance with claim 6, wherein the step ofprocessing said first and second signals comprises the steps of using anadaptive filter to filter out noise.
 9. A method in accordance withclaim 6, wherein the step of processing said first and second signalscomprise the steps of using one or more noise-canceling algorithms foreliminating one or more undesired frequency components.
 10. A method inaccordance with claim 9, wherein said one or more noise-cancelingalgorithms are effective to: A. extract said one or more undesiredfrequency components; B. invert said extracted frequency components; andC. generate one or more signals that cancels said one or more undesiredfrequency components.
 11. A method in accordance with claim 6, whereinsaid respiratory motion is characterized by a respiratory cycle, andwherein said first correction factor is a relatively static factor thataccounts for motion of said target during only a selected portion ofsaid respiratory cycle.
 12. A method in accordance with claim 11,wherein said selected portion of said respiratory cycle is centeredabout a peak within said cycle.
 13. A method in accordance with claim 6,wherein the step of generating said first correction factor comprises:digitally comparing said one or more near real-time x-ray images withsaid pre-operative 3D scan so that the difference in position betweenthe position of the target in the 3D scan as compared to the position ofthe target in said real-time x-ray images can be computed.
 14. A methodin accordance with claim 13, wherein the step of digitally comparingsaid near real-time x-ray images includes the steps of: A. generatingone or more DRRs using the 3D scan together with said known beam pathsand intensities of said x-ray imaging beams; B. computing the changes inposition and orientation of said target that are necessary in order tobring said one or more DRRs in registration with said one or morereal-time x-ray images.
 15. A method in accordance with claim 1, whereinsaid radiosurgical beams are x-rays.
 16. A method in accordance withclaim 1, wherein said treatment plan contains information regarding thenumber, intensities, positions, and directions of said beams that areeffective to create said at least one lesion.
 17. A method in accordancewith claim 3, further comprising the step of implanting a plurality offiducials within said surrounding region proximate to said target,before taking said pre-operative 3D scan, so that said position of saidtarget as indicated in said pre-operative 3D scan is the position of thetarget relative to said plurality of fiducials.
 18. A method of treatinga moving target in a patient by applying one or more radiosurgicalbeams, generated from a radiosurgical beam source, to said target, themethod comprising the steps of: A. generating a treatment plancontaining information defining the positions, angles, and intensitiesof one or more radiosurgical beams that are adapted to create, whenapplied to said target, at least one radiosurgical lesion, saidtreatment plan being based on 3D scan data that indicates the positionof said target at treatment planning time; B. in near real time,monitoring the motion of said target to determine the difference betweenthe position of the target at a current time, as compared to theposition of said target at treatment planning time as indicated by said3D scan data; C. in near real time, adjusting the relative position ofthe radiosurgical beam source and said target to account for thedifference in target position using a robotic controller; and D.applying one or more radiosurgical beams from said adjusted position ofsaid radiosurgical beam source.
 19. A method in accordance with claim18, wherein said motion of said target is caused by the respiration andthe heart beat of said patient; and wherein the step of adjusting saidrelative position of said radiosurgical beam source to account for thedifference in target position comprises: A. sensing the motion of saidtarget during a relatively short time interval, using a breathing sensorand a heart beat sensor; B. extrapolating said motion into a completecycle; and C. synchronizing said robotic controller with saidextrapolated motion of said target.
 20. A method of treating a targetregion in a patient using radiosurgery, comprising the steps of: A.generating 3D scan data representative of a three dimensionalpre-operative image of said target region and of adjacent tissue, saidtarget region undergoing a motion; B. based on said 3D scan data,generating a treatment plan defining a plurality of x-ray beamsappropriate for creating at least one lesion on said target region; C.in near real time, determining the position of said target region, andgenerating data representative of the change in the position of saidtarget region at a current time compared to the position of said targetregion in said CT scan; D. in near real time, generating said pluralityof x-rays with an x-ray source and applying said x-rays to said targetregion in such a way that said x-ray source tracks said motion of saidtarget region, while maintaining substantially the same treatment plan.21. A system for treating a moving target in a patient by forming aradiosurgical lesion on said target, the system comprising: A. anapparatus for generating 3D scan data representative of a pre-operative3D diagnostic image of said target and a surrounding region; B. aprocessor including treatment planning software for generating, based onsaid 3D scan data, a base treatment plan defining a plurality of x-raybeams appropriate for creating at least one lesion in said target; C. abeam source for generating one or more radiosurgical beams adapted tocreate at least one lesion in said target; D. a positioning system thatcontrols the relative position of said beam source and said target; E.imaging means for generating at least one real-time x-ray image of saidtarget; F. means for sensing the motion of said target, and forgenerating at least one signal representative of said motion; and G.means for generating from said at least one signal at least onecorrection factor that is effective, when applied to said positioningsystem, to modify the position of said beam source relative to saidtarget so as to accommodate for the difference in position of saidtarget at a current time as compared to the position of said target insaid pre-operative diagnostic image.
 22. A system in accordance withclaim 21, further comprising: A. a signal processor for processing saidat least one signal to generate a first signal substantiallycharacterized by a frequency F1, and a second signal substantiallycharacterized by a frequency F2; B. means for generating from said firstsignal a first correction factor, and for generating from said secondsignal a second correction factor; and C. means for superposing saidfirst correction factor and said second correction factor to obtain saidcorrection factor that is effective, when applied to said positioningsystem, to modify the position of said beam source relative to saidtarget so as to accommodate for the difference in position of saidtarget at a current time as compared to the position of said target insaid pre-operative diagnostic image.
 23. A system in accordance withclaim 21, wherein said motion of said target is caused by respiration ofsaid patient and by the pumping of the heart of said patient, andwherein said means for sensing the motion of said target includes abreathing sensor for sensing the respiration of said patient, and aheart rate monitor for monitoring the cardiac pumping of said patient.24. A system in accordance with claim 22, wherein said frequency F1 isrepresentative of the respiratory motion of said patient, and saidfrequency F2 is representative of the cardiac pumping motion of saidpatient.
 25. A system in accordance with claim 22, wherein said signalprocessor comprises: A. means for splitting said at least one signalinto first and second signals; B. means for processing said first andsecond signals to remove undesired components from each signal, so as togenerate said first signal substantially characterized by a frequencyF1, and said second signal substantially characterized by a frequencyF2.
 26. A system in accordance with claim 25, wherein said means forprocessing said first and second signals comprises an adaptive filterfor filtering out noise.
 27. A system in accordance with claim 25,wherein said means for processing said first and second signalscomprises software that includes one or more noise-canceling algorithmsfor eliminating one or more undesired frequency components, and whereinsaid one or more noise-canceling algorithms are effective to: A. extractsaid undesired frequency components; B. invert said extracted frequencycomponents; and C. generate one or more signals that cancel saidundesired frequency components.
 28. A system in accordance with claim22, wherein said first correction factor is a relatively static factorthat accounts for motion of said target during only a portion of saidrespiratory cycle.
 29. A system in accordance with claim 22, whereinsaid means for generating said first correction factor comprises meansfor digitally comparing said one or more near real-time x-ray imageswith said pre-operative 3D scan so that the difference in positionbetween the position of the target in the 3D scan as compared to theposition of the target in said real-time x-ray images can be computed.30. A system in accordance with claim 21, wherein said positioningsystem is an industrial robot having an articulated arm assembly, andwherein said beam source is an x-ray linac mounted at one end of saidarticulated arm assembly of said robot.
 31. A system in accordance withclaim 21, wherein said positioning system is effective, in response toreceipt of said correction factor, to modify the position of said beamsource in such a way that said beam source tracks the motion of saidtarget.
 32. A system in accordance with claim 21, wherein said imagingmeans comprises: A. one or more x-ray sources for generating x-rayimaging beams; and B. one or more corresponding x-ray detectors fordetecting said imaging beams after said beams have traversed saidtarget.
 33. A system in accordance with claim 29, wherein said means fordigitally comparing said one or more near real-time x-ray images withsaid 3D scan comprises: A. means for generating one or more DRRs usingthe 3D scan together with information regarding the beam paths andintensities of said x-ray imaging beams; and B. computing the changes inposition and orientation of said target that are necessary in order tobring said one or more DRRs in registration with said one or morereal-time x-ray images.
 34. A system in accordance with claim 21,wherein said 3D scan data comprise at least one of: CT scan data; PETscan data; and MRI scan data.
 35. A system in accordance with claim 34,wherein said apparatus for generating 3D scan data comprises at leastone of: a) a CT scanner; b) a PET scanner; and c) an MRI scanner.
 36. Asystem in accordance with claim 21, wherein said 3D scan data compriseat least one of CT scan data, PET scan data, and MRI scan data.